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Are There Any Side Effects Of The Flu Shot?

Overview of the Flu Shot

Every year, people all over the world take the flu vaccine to protect themselves from influenza or the flu.(1,2,3) The flu shot is a vaccine that is usually injected into the arm, but it can also be administered as a nasal spray. The flu vaccine is known to reduce the chances of getting the flu by nearly 60%.(4)

While flu shots are typically considered to be relatively safe, any side effects happening due to the flu shot are usually mild. However, in some rare cases, there can be severe side effects. This is why it is important that before getting your flu shot, you should be aware of what to expect.

A mercury-based preservative known as thimerosal is used in the production of some multi-dose vials of the flu vaccine. Thimerosal is used to prevent the growth of bacteria and other germs. According to the Centers for Disease Control and Prevention, thimerosal use in vaccines is known to be safe, and it causes few side effects.(5) If you have concerns about thimerosal, you can request your doctor for a vaccine that does not contain it.

Here are some of the most common side effects of the flu vaccine that some people may experience.

Are There Any Side Effects Of The Flu Shot?

Are There Any Side Effects Of The Flu Shot?

Common Side Effects Associated With The Flu Shot

Most of the common side effects of the flu shot are mild and are the same in babies, children, and adults. These include:

  • Reaction At The Injection Site: Having a reaction at the injection site is the most common side effect of getting the flu shot. This happens most commonly on the upper arm. Once the vaccine is given, you may experience some soreness, redness, slight swelling, and warmth. These effects tend to last for less than two to three days. To decrease the discomfort, you can consider taking some ibuprofen before getting the flu shot.
  • Aches and Pains and Headache: After getting your flu shot, you may experience some aches and pain in the muscles throughout the body or have headaches. This is more likely to happen on the first day and go away within the next two days. To ease your discomfort, you can take pain relievers, but there is a lot of debate on whether it is safe to take ibuprofen or acetaminophen to treat vaccine-related side effects. Some research shows that taking these medications may change or reduce how the body responds to the vaccine.(6) In fact, one study carried out on children discovered that taking ibuprofen or acetaminophen did not decrease the body’s response to the flu shot.(7) However, studies have found conflicting data, due to which it is still unclear whether you should take these medications or not.
  • Fever: Getting a fever of 101oFahrenheit (28oCelsius) or a low-grade fever is a common side effect of the flu shot. Having a slight fever is considered to be a minor side effect and goes away within a day or two. If the fever causes too much discomfort, you can take ibuprofen or acetaminophen, but as mentioned above, there are some concerns about taking these medications.
  • Fainting or Dizziness: While it is rare, but some people may experience fainting or dizziness after taking the flu shot. These side effects, however, should not last longer than a day or two. If you have a history of fainting or getting dizzy while getting an injection, you should let your doctor know before getting the flu shot.

Serious Side Effects Associated with the Flu Shot

While serious side effects are rare after getting the flu shot, but they may include:

1. Severe Allergic Reactions

In very rare cases, the flu vaccine can cause a severe allergic reaction in some people. Severe allergic reactions tend to happen within a couple of hours of getting the vaccine.(8) Symptoms of severe allergic reactions may include:

  • Swelling
  • Hives
  • Fast heart rate
  • Dizziness
  • Weakness
  • Trouble breathing

If you experience any of these symptoms, you should call your doctor immediately. If they are severe enough or you are having trouble breathing, you should call your local emergency number or head to the closest emergency room.

2. High Fever

Having a fever higher than 101oF (38oC) is rare, and if you have a high fever, you should immediately call your doctor.

3. Guillain-Barré Syndrome

In extremely rare cases, some people who have gotten the flu shot have gone on to develop Guillain-Barré syndrome. The Guillain-Barré syndrome is a type of neurological condition that causes paralysis and weakness throughout the body. However, to date, it is not clear if the flu shot is actually responsible for causing Guillain-Barré syndrome in these cases.(9,10,11)

People who have had Guillain-Barré syndrome in the past are more likely to develop the condition after getting vaccinated. It is, therefore, important to let your doctor know if you have a history of Guillain-Barré syndrome. Nevertheless, having Guillain-Barré syndrome in the past does not automatically mean that you cannot receive the flu shot. You can talk to your doctor and find out if it is safe for you to take the flu vaccine.

If you develop the symptoms of Guillain-Barré syndrome after receiving the flu shot, you should immediately call your doctor or your local emergency number. Avoid driving if you feel muscle weakness setting in and call for help.

Who Should Get The Flu Shot?

The flu shot is generally recommended for everyone who is 6 months or older. People who are at risk of developing some serious complications from having the flu should also receive the flu vaccine. This include:

    • Pregnant women
    • People who have chronic health conditions and their caregivers
    • People aged 65 years and older

However, the flu shot is not recommended for the following people:

  • Who have had an allergic reaction to the flu shot in the past.
  • Who are currently sick and have a moderate to high fever.
  • Who has a severe allergy to eggs.(12,13)


The flu shot is a safe and effective treatment that helps you avoid many strains of the flu virus. The flu vaccine is associated with very few side effects, and that also rarely. If you are concerned about the side effects of taking a flu shot, you should talk to your doctor. Your doctor can help you decide if taking the flu shot is right for you. However, people having a moderate to severe allergy to eggs should avoid getting the flu shot. Still, your doctor would be the best person to decide if you would be a good candidate for the flu shot or whether you should avoid taking it.


  1. Eisenstein, M., 2019. Towards a universal flu vaccine. Nature, 573(7774), pp.S50-S50.
  2. Cdc.gov. 2021. Vaccine Effectiveness: How Well Do the Flu Vaccines Work? | CDC. [online] Available at: <https://www.cdc.gov/flu/vaccines-work/vaccineeffect.htm?> [Accessed 1 April 2021].
  3. Who.int. 2021. Vaccines and immunization: What is vaccination?. [online] Available at: <https://www.who.int/news-room/q-a-detail/vaccines-and-immunization-what-is-vaccination?adgroupsurvey> [Accessed 1 April 2021].
  4. Cdc.gov. 2021. CDC Seasonal Flu Vaccine Effectiveness Studies | CDC. [online] Available at: <https://www.cdc.gov/flu/vaccines-work/effectiveness-studies.htm> [Accessed 1 April 2021].
  5. Cdc.gov. 2021. Thimerosal and Vaccines | Vaccine Safety | CDC. [online] Available at: <https://www.cdc.gov/vaccinesafety/concerns/thimerosal/index.html> [Accessed 1 April 2021].
  6. Saleh, E., Moody, M.A. and Walter, E.B., 2016. Effect of antipyretic analgesics on immune responses to vaccination. Human vaccines & immunotherapeutics, 12(9), pp.2391-2402.
  7. Walter, E.B., Hornik, C.P., Grohskopf, L., McGee, C.E., Todd, C.A., Museru, O.I., Harrington, L. and Broder, K.R., 2017. The effect of antipyretics on immune response and fever following receipt of inactivated influenza vaccine in young children. Vaccine, 35(48), pp.6664-6671.
  8. James, J.M., Zeiger, R.S., Lester, M.R., Fasano, M.B., Gern, J.E., Mansfield, L.E., Schwartz, H.J., Sampson, H.A., Windom, H.H., Machtinger, S.B. and Lensing, S., 1998. Safe administration of influenza vaccine to patients with egg allergy. The Journal of pediatrics, 133(5), pp.624-628.
  9. Haber, P., DeStefano, F., Angulo, F.J., Iskander, J., Shadomy, S.V., Weintraub, E. and Chen, R.T., 2004. Guillain-Barré syndrome following influenza vaccination. Jama, 292(20), pp.2478-2481.
  10. Hahn, A.F., 1998. Guillain-barré syndrome. The lancet, 352(9128), pp.635-641.
  11. Lasky, T., Terracciano, G.J., Magder, L., Koski, C.L., Ballesteros, M., Nash, D., Clark, S., Haber, P., Stolley, P.D., Schonberger, L.B. and Chen, R.T., 1998. The Guillain–Barré syndrome and the 1992–1993 and 1993–1994 influenza vaccines. New England Journal of Medicine, 339(25), pp.1797-1802.
  12. Krietsch Boerner, L., 2020. The Flu Shot and the Egg.
  13. Boerner, L.K., 2020. The flu shot and the egg. ACS Central Science, 6(2), p.89.
Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:June 3, 2022

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